Many attempts have been made to devise laminating resins having low volatile emissions and still meet the physical specifications and other desirable properties of the end products, while remaining relatively easy to use. In Lee U.S. Pat. No. 4,465,806, for example, a more or less conventional unsaturated polyester resin is combined with, instead of the usual styrene, a reaction product of a polyepoxy compound and acrylic or methacrylic acid which may be the diacrylate of a polyglycidyl ether of bisphenol-A. These compounds are made from epoxy compounds, and the author of U.S. Pat. No. 4,465,806 requires that a significant portion of the epoxy groups be unreacted for use in their resin. Moreover, unlike the present invention, they form pendant OH groups.
Ethoxylated, difunctional, bisphenol-A has been used in the past as an ingredient in various types of resins, generally resins which include a significant diisocyanate component, as in Ford, Jr. et al U.S. Pat. No. 3,876,726.
European Patent Application 0 234 692 discloses a composition said to be useful as a molding resin, having the virtue of a low residual monomer concentration in the final product. The gist of the disclosure appears to be that dimethacrylates such as ethoxylated bisphenol-A dimethacrylate can be used as components of otherwise more or less conventional unsaturated polyester resins to reduce the amount of residual styrene monomer in contained molding processes such as cell molding, compression molding, and sheet molding. See also Reid and Rex U.S. Pat. No. 5,202,366, which includes a low-profile additive in a similar composition.
Laminating resins are expected to cure relatively quickly, since they are (typically) sprayed in many layers. Moreover, they cure at ambient temperatures rather than elevated temperatures such as are used in confining molds. In addition, as will be shown later herein, many monomers, such as vinyl and acrylic monomers, may not be compatible with the base resin. Thus it is difficult to design a good laminating resin satisfying the many commonly recognized desirable criteria.
The daunting problem of volatile emissions during spray-up or other laminating procedures has until now been unsolved. Applicants' dramatic results detailed herein show that lamination can be used with significantly reduced emissions in the workplace.